An electrical discharge machine is commonly equipped with a power supply for providing high-frequency machining pulses to the dielectric filled machining gap formed between the tool electrode and the workpiece in a dielectric containing or collecting work vessel. In conventional EDM power supply circuit arrangements and methods, machining power pulses are produced in a unit (power supply unit) provided separately from the machine proper which carries mechanical components and the work vessel in which the machining gap is defined between the tool electrode and the workpiece. The separate power supply unit is adapted to package in its cabinet all principal electrical components required to produce at its output a succession of unidirectional power pulses of a predetermined polarity relative to the tool electrode and the workpiece, the output of the unit being connected and hence the power pulses outgoing from the unit being transmitted to the machining gap by way of a elongated cable or line which must be provided. As a consequence, stray resistance and inductance included in the cable or line impede transmission of the unidirectional electric power and act to cause a considerable loss of power and distortion of pulse waveform transmitted to the machining gap. It has, therefore, been unavoidable for the material removal to be undesirably limited, for the machining efficiency to be unsatisfactorily low and for the entire power unit to become excessively large and bulky in conventional electrical discharge machines.